Electric machines are used in the automotive technology industry by way of example for braking systems and/or steering systems of motor vehicles. Control devices that are embodied so as to operate the electric machines frequently comprise an inverter and can thus be influenced on the input side with a direct current and a direct voltage. This is advantageous in the case of being used in motor vehicles in which the vehicle electrical system provides both a direct voltage as well as a direct current.
The presence of an essentially constant power requirement of an electric machine of a motor vehicle and simultaneously a low voltage of the energy supply increases the current that is to be supplied. One consequence of the increased current is an increased heating of the electronic system of the direct current side or direct voltage side, said electronic system being used to control the machine. If the electronic components of the electronic control system are not designed for a continuously increased current, said components can become damaged. The load on the vehicle electrical system is increased as a result of the current consumption increasing in this manner and as a result of the further reducing supply voltage.
DE 10 2007 017 296 A1 discloses a method for operating an electric machine in which an estimated value of a prevailing direct current input of a control device is ascertained by an observer on the basis of modeled and in particular temperature-variable parameters, wherein a temperature dependency is compensated for on the basis of the temperature values that are ascertained. A difference between a predetermined maximum value of the direct current input and the estimated value of the direct current input is used as an input variable of an integral controller, wherein the output signal of said integral controller is supplied to a limiter. The output signal of the limiter is in turn used to set a direct threshold value of the alternating current that influences a desired value for setting the d-motor current or the q-motor current. If the estimated value of the direct current input is greater than the predetermined maximum value, the direct threshold value of the alternating current is reduced. However, particularly precise knowledge regarding the temperature behavior of the respective electronic components and also a temperature measurement are required, this necessitates an increased outlay and owing to the reduced complexity of the model with respect to reality is not sufficiently accurate for future motor vehicle systems.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.